As one of safety systems in vehicles, an alarm system for warning that a seat belt is not worn during ride is practically used. This alarm system warns when wearing of the seat belt is not sensed in a state where sitting of a person is sensed. As a device for sensing sitting of a person, a load-detecting device for detecting a load due to sitting may be used.
Some of such load-detecting devices may be disposed under a seat cushion of a seat. In a seat device, a seat cushion may be disposed on a seat pan, or a seat cushion may be disposed on a plurality of S springs fixed to a frame. In a seat device in which a seat cushion is disposed on a plurality of S springs, a load-detecting device may be engaged with the S springs. Patent Literature 1 listed below describes a sitting detection device as such a load-detecting device. The sitting detection device disclosed in Patent Literature 1 includes a base engaged with S springs and a membrane switch disposed on the base through a spacer.    [Patent Literature 1] JP-A-2011-105278